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Changing Skyline: Arch St.'s a bad place for ultra-tall and dense tower

tly, fans swarmed the meeting room, hoisting printed signs as if they were rally towels.

What is it about a really tall skyscraper that makes people fall into a swoon?

Ever since developers unveiled their design for a 1,500-foot office tower called the American Commerce Center, supporters have been behaving like teenage girls at the opening of Twilight. When the Philadelphia Planning Commission held a hearing on the project recently, fans swarmed the meeting room, hoisting printed signs as if they were rally towels.

"BUILD IT!" the signs demanded in upper-case letters. The accompanying rendering depicted the slick glass behemoth towering over a puny Comcast Center.

Yes, they should build it. But let's hope city officials make them build it better.

Like the smitten everywhere, partisans of the American Commerce Center (ACC) are inclined to offer their love unconditionally. They're so entranced by the record-breaking stature of the proposed skyscraper that they seem not to have noticed that the object of their affection is a fat, hulking copycat.

It's not like the city hasn't been accommodating. This week, City Council's rules committee endorsed a bill to increase the height allowance at 18th and Arch Streets, a move that virtually guarantees final passage by the full membership this month. The increase, to a generous C5 classification, is the first of two zoning changes required before the ACC tower can soar past the reigning height champ, the 975-foot Comcast building.

Fortunately, the new zoning designation won't take effect until city planners approve a final architectural design. The negotiations will be a crucial test of Mayor Nutter's campaign promise to allow planners a free hand with developers.

Their goal should be to put this complex on Slim-Fast. There's nothing inherently wrong with a 1,500-foot skyscraper downtown - assuming the developer can find tenants to populate it. Dense mixed-use projects are good for cities and good for the environment. They bring people and activity, while deterring sprawl elsewhere.

But it is possible to have too much density. ACC's developers, led by Hill International, are attempting to pack in way more stuff - 2.2 million square feet - than the modest 1.5-acre site can handle. Along with the office tower, they envision a 477-foot-high interlocking hotel, a six-level shopping mall, movie theaters, meeting rooms, and a 369-car underground garage.

If you want to get a sense of ACC's enormity, look at Manhattan's Time Warner Center, which features a virtually identical menu of uses. Time Warner contains more space, 2.8 million square feet, but its two 750-foot towers rest on a generous 3.4 acres. Not only is that site twice the size, it overlooks the open expanse of Columbus Circle and Central Park.

What's the harm of overbuilding at 18th and Arch? That little intersection - where the multicolored Arch Street Presbyterian Church gamely clings to the southeast corner - is already hemmed in by the immense towers of Comcast, Bell Atlantic and Two Logan Square. Comcast plans a second, sizable tower at 18th and Market. When developer Ron Caplan tore down a couple of perfectly nice 19th-century houses at 19th and Arch this fall, he was obviously setting up his block for a high-rise, too.

Such a concentration might be acceptable on the wide streets of Market, Broad and JFK Boulevard. But Arch Street, one of Philadelphia's colonial-era thoroughfares, is just 36 feet wide curb to curb. If the ACC overloads its site, the city will create its own version of Wall Street's oppressive, sunless canyons.

It won't be easy to talk the developers down from their ambitious goals. At this point, most builders would have prepared only basic massing studies. But the center's designers - Philadelphia-born architect A. Eugene Kohn and William C. Louie, of New York's KPF Associates - have already produced a stack of detailed drawings for the intricate project. The developers have spent more than $2 million, according to their attorney Peter F. Kelsen.

The designs, however, are predicated on a wildly optimistic set of assumptions.

This is how the city's zoning code works for high-rises: Developers start with a basic envelope of square footage, tied to a site's zoning classification. Then they attempt to enlarge the envelope by accruing bonus points for public amenities like open space or transit connections.

ACC's developers assume their project will qualify for every available bonus the city offers, and then some. Once Council upgrades their site's zoning, they plan to lobby for another bill that would let them apply for even more bonus points.

Skyscraper developers are famously creative when it comes to proposing bonus amenities. You have to wonder about the viability of ACC's.

Will people really trek to the sixth floor to sit in the public sculpture garden? Who's going to provide the art and lease the adjacent gallery? And does Hill International really expect to operate a six-level shopping mall with no atrium to provide visual connections between floors? The company seems to believe the zoning code can be customized to fit whatever design it pulls out of a hat.

Piling on so much space has made KPF's tower design morbidly obese. The Comcast tower at least has the grace to narrow on its way to the sky, and its corner pleats help slim down its bulk. KPF merely slices off a few token angles on the north side. The American Commerce Center pretty much rises straight and sheer, with no setbacks. At 1,200 feet, the roof angles back, and the architects stick in a giant cocktail straw - a 300-foot spire. ACC's sheer walls would resemble Comcast's bad side, the vertical ice rink on Arch Street.

Since presenting the design, KPF has significantly improved the detailing of the glass curtain wall, which now has some much-needed texture. But the design is still a compendium of borrowed architectural moves - the crown from Daniel Libeskind's Freedom Tower in New York, the hotel bridge and giant opening from Rem Koolhaas' CCTV headquarters in Beijing.

In trying to sell their tower to the city, ACC's developers argue they'll create a Philadelphia icon. But you can't make an icon by copying someone else's design.